There are liquid medicament compositions that degrade and lose their potency over time, before they can be administered to a patient.
In order to handle these medicament compositions, so called multi chamber medicament containers have been developed. They often comprise elongated tubular containers divided by movable stoppers into a number of compartments or chambers, where the medicament in powder form is placed in one chamber and a diluent is placed in another chamber. At certain positions along the containers, passages are arranged, wherein, when the stoppers are moved, the passages are opened, allowing communication between the chambers and thus a mixing between the medicament and the diluent. The stoppers are often moved by an elongated plunger rod, which is often actuated by a drive spring.
After mixing, a priming sequence is often necessary, in which air and gas entrapped in the medicament container after mixing needs to be removed. The stoppers have to be moved a short distance by the plunger rod in order to remove the air. The injection sequence is performed after mixing and priming.
One problem with devices handling dual chamber medicament containers is that the devices tend to be rather long because the plunger rods have to be moved in the longitudinal direction of the devices both for priming, mixing and injection if the same drive springs are to be used for all the sequences. Also, a mechanical solution allowing the plunger rod to be actuated and stopped at several instances usually requires rather complex mechanisms.
The document U.S. Pat. No. 8,323,238 discloses a medicament delivery device arranged to handle multi-chamber containers. However it contains only one drive spring and will therefore be rather long. Its length is not altered during use of the device.
The document U.S. Pat. No. 8,123,719 discloses a medicament delivery device employing several drive springs in order to perform different required functions. However, the device is bulky and not intended for personal use by patients without medical training.